#define  _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;

class A
{
public:
	A() = default;

	A(const int& a)
		:_a(a)
	{}


private:
	int _a = 10;
};

int main()
{
	A a1;
	A a2(a1);
	
	return 0;
}